In connection with a conventional two-stroke cycle engine provided with a crank chamber, an intake port having an opening which is open to the crank chamber is communicated with an intake passage. A scavenge port and an exhaust port are also opened within the peripheral wall of the cylinder. The exhaust port is communicated with an exhaust passage and the scavenge port is provided with a scavenge passage communicating with the crank chamber. The scavenge port and the exhaust port are opened and closed at predetermined times by means of the displacement of a piston disposed in association with each cylinder so that the fresh air-fuel mixture, called merely the mixture hereinafter, sucked into the crank chamber through means of the intake port is compressed as a result of the lowering of the piston and the compressed mixture is fed into the cylinder chamber through means of the scavenge port and then exhausted through means of the exhaust port.
With the two-stroke cycle engine having the structure described above, however, there is developed a spitting phenomenon in which the mixture conducted into the crank case is reversely conducted into a carburetor by means of the pressure of the piston.
For example, with the multiple cylinder two-stroke cycle engine, pressure variations, that is, pulsations, are caused by means of the rotation of the crank shaft, within the respective intake passages and, hence, the fresh mixture is accordingly pulsated. In the instance that this pulsation is substantially large, the spitting phenomenon of the fresh mixture may develop within the intake passages. This may result in the fluctuation of the air/fuel ratios of the fresh mixtures conducted into the respective cylinders.
Furthermore, there is also provided a multiple cylinder two-stroke cycle engine having intake passages injectors are arranged in place of the carburetors upon the upstream sides of lead valves.
With the engine of this type, in the case where the fuel is injected simultaneously from the respective injectors during the neutral or low revolution operation of the engine, an instance may occur wherein the fuel injection timing accords with the generation of the reverse flow of the fresh mixture within a particular one of the multiple cylinders. In such a case, air and fuel adversely flow from that cylinder into the other cylinders in which the fuel injection accords with the rectification of the mixture.
During the engine operation periods at the neutral or low revolution number values or levels of the engine, the fuel injection time is short, so that when the air and fuel are not uniformly distributed or conducted into the respective cylinders the concentration of the mixture differs within the different cylinders and, the injection and the rectification of the fuel mixture within the other cylinders are carried out during the same time periods. This adversly results in the fluctuation of the air/fuel ratio of the fresh mixture with respect to the respective cylinders.
Such adverse phenomenon may be caused in a case where the fuel injectors are arranged upon the downstream side of the lead valves.